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Osteochondral graft and method of use for repairing an articular cartilage defect site

Osteochondral graft and method of use for repairing an articular cartilage defect site description/claims

This application contains subject matter which is related to the subject matter of the following application, which is hereby incorporated herein by reference in its entirety:

“Shaped Osteochondral Grafts and Methods of Using Same,” by McKay, U.S. Ser. No. 11/120,136, filed Apr. 30, 2005.

The present invention relates generally to the field of grafting for articular cartilage repair, and more particularly, to a novel configured osteochondral graft and its use in articular cartilage resurfacing repair of a host defect site in a mammal.

Human joint surfaces are covered by articular cartilage that provides a resilient, durable surface with low friction. Cartilage is an avascular tissue that has a small number of chondrocytes encapsulated within an extensive extracellular matrix. The cartilage acts to distribute mechanical forces and to protect subchondral bone. For example, the knee is a particular instance of a cartilage surfaced (the condyle) bone area. The knee comprises three bones—the femur, tibia, and patella that are held in place by various ligaments. Corresponding chondral areas of the femur and the tibia form a hinge joint and the patella acts to protect the joint. Portions of the chondral areas as well as the undersurface of the patella are covered with articular cartilage that allows the femur, patella and tibia to smoothly glide against each other without causing damage.

Damage to the articular cartilage, subchondral bone or both can result from traumatic injury or a disease state. For example, articular cartilage in the knee can be damaged due to traumatic injury as with athletes and via a degenerative process as with older patients. The knee cartilage does not heal well due to the lack of vascularity. Hyaline cartilage in particular has a limited capacity for repair and lesions in this material, without intervention, can form scar tissue lacking the biomechanical properties of normal cartilage.

A number of procedures are used to treat damaged articular cartilage. Currently, the most widely used procedure involves lavage, arthroscopic debridement and repair stimulation. Repair stimulation is conducted by several methods including, drilling, abrasion arthroplasty and microfracture. The goal of these procedures is to penetrate into subchondral bone to induce bleeding and fibrin clot formation. This reaction promotes initial repair. However, the resulting formed tissue is often fibrous in nature and lacks the durability of normal articular cartilage.

In an attempt to overcome the problems associated with the above techniques, osteochondral transplantation, also known as “mosaicplasty” or “OATS” has been used to repair articular cartilage. This procedure involves removing injured tissue from the articular defect and drilling cylindrical openings in the area of the defect and underlying bone. Solid cylindrical plugs, consisting of healthy cartilage overlying subchondral bone, are harvested from another area of the patient, typically from a lower weight-bearing region of the joint under repair, or from a donor patient, and are implanted in the host openings. However, in these cases, if the opening is too large, the graft can rotate or move within the host site and become loose, which will prevent bio-ingrowth with the surrounding tissues. Further, if the host site is too small, significant tissue and cellular damage can occur to the graft during the implantation.

Historically, osteochondral grafting has been used successfully to repair chondral damage and to replace damaged articular cartilage and subchondral bone. First, in this procedure, cartilage and bone tissue of a defect site are removed by routing to create a cylindrical bore of a precise geometry. Then a cartilage and subchondral bone plug graft is harvested in a matching geometry. The donor plug graft is typically removed from another body region of less strain. The donor plug graft can be harvested from a recipient source (autograft) or from another suitable human or other animal donor (allograft and xenograft respectively). The harvested plug graft is then implanted into the bore of the routed defect site. Healing of the plug graft to the host bone results in fixation of the plug graft to the surrounding host region.

Success of the grafting process is dependant on the intimate seating and sizing of the graft within the socket. First, surface characteristics of the plug graft are critical. For the procedure to be successful, the surface of the transplanted plug graft must have the same contour as the excised osteochondral tissue. If the contour is not a correct match, a repaired articular surface is at risk for further damage during patient ambulation. Additionally, some graft shapes do not pack well into irregular defects. The graft may have a propensity to rotate resulting in poor integration of the graft to the surrounding host tissue. An improperly placed and sized plug graft can result in host tissue integration failure and post implantation motion with associated articular surface collapse.

Accordingly, there is a need for an improved and/or alternative shaped osteochondral graft and an associated implantation technique, for repairing articular cartilage defects.

The present invention comprises an osteochondral graft for use in repairing an articular cartilage defect site in a mammal. The osteochondral graft disclosed herein employs a cartilage cap that has a certain thickness with top and bottom surfaces and a wall extension projecting from the cartilage cap. The wall extension has an external surface and an internal surface, with the internal surface at least partially defining an internal space. The osteochondral graft is implanted to repair an articular cartilage defect site following the removal of damaged and/or diseased articular cartilage.

More particularly, the present invention provides in one aspect, an osteochondral graft configured for repairing an articular cartilage defect site. The osteochondral graft includes a cartilage cap and a wall extension, with the cartilage cap having a top surface and a bottom surface and the wall extension projecting from the bottom surface of the cartilage cap. The wall extension includes an external surface and an internal surface with the internal surface at least partially defining a centralized internal space. The wall extension and internal space are sized and configured to facilitate the implantation of the osteochondral graft into the articular cartilage defect site.

The present invention provides in another aspect, an osteochondral graft configured for repairing an articular cartilage defect site. The osteochondral graft includes a cartilage cap and a wall extension, with the cartilage cap having a top surface and a bottom surface, with the wall extension projecting from the bottom surface of the cartilage cap. The wall extension includes an external surface and an internal surface with the internal surface at least partially defining a centralized internal space. The osteochondral graft further includes a central axis that extends between the cartilage cap and the proximal end of the wall extension. Either the internal surface and/or the external surface may be tapered at a taper angle relative to the central axis. This taper angle assists the user when inserting the osteochondral graft into the surgically prepared articular cartilage defect site.

Another aspect of the present invention provides a method for repairing an articular cartilage defect site in a mammal, the method includes surgically creating an opening in the articular cartilage defect site. The opening includes a centrally positioned platform and a channel that is circumferential relative to the platform and extends to a certain depth below the articular cartilage defect site. The method also includes employing an osteochondral graft that includes a cartilage cap and a wall extension. The cartilage cap has a top surface and a bottom surface with the wall extension projecting from the bottom surface of the cartilage cap. The wall extension also has an external surface and an internal surface. The internal surface at least partially defines or bounds a centralized internal space. The method provides further for implanting the osteochondral graft into the opening. The osteochondral graft is properly sized and configured to be inserted into the surgically created opening. After being implanted, the bottom surface of the cartilage cap of the osteochondral graft will contact the centralized platform of the opening and the wall extension will have slid into the channel of the opening. The configuration of the cartilage cap and the wall extension will promote and enhance bio-ingrowth between the implanted osteochondral graft and the opening.

Further, additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.

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• Utility Patent

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